‘So to be clear,’ Grove went on, ‘you are now saying it was a set-up, right from the start. A great big Fabergé egg of a fake. Far from being rivals, the GRU worked with the SVR to sell us – to sell you – the mother and father of all intelligence dummies. The prime minister was never working for the Russians, the sex video was a fake, Stuart was the only agent working in Whitehall – and he was easily expendable in the cause of creating terrible chaos, confusion and mistrust at the heart of our democratic system?’

It was a moment before Kate realized Grove was expecting an answer. She certainly was exacting her pound of flesh. ‘Yes,’ Kate said. ‘Absolutely.’

If the price of escaping all this was to flip everything she really believed on its head, she might as well do it with conviction.

‘Sergei was killed just in case he blurted out the real truth to you on the train – that you had been deceived and manipulated right from the start?’

‘Yes,’ Kate said again, with excessive conviction. ‘That is correct.’

Grove tapped her pen on the file. ‘A cynic might note, Mrs Henderson, that you have announced you wish to leave the service with immediate effect. This way, the case is conveniently closed. There will be no committee of inquiry, no torturous, complicated, draining search for the truth. Just closure. The prime minister recovers his reputation, the Service can move on and you . . . well, you walk away, with your reputation and references intact. Free as a bird, one might say.’

‘I’m not a cynic,’ Kate said. And when she realized that Grove had truly no sense of humour, she went on: ‘Ian was right all along. It’s not easy to admit that, but it’s true.’

If nothing else, she thought, she was becoming a much better bloody liar.

‘We shouldn’t blame Kate in any way,’ Suzy chipped in. ‘It was all so plausible. Who wouldn’t have jumped at such a sensational story? If true, it would have been the most amazing intelligence coup of the modern era, enough to make anyone’s career.’

Kate didn’t dignify this with an answer.

Grove leant forward, her reading glasses brushing against her clipboard. There were a lot of ticks on her checklist now. ‘After all this,’ she said, ‘you suddenly wake up one day and decide that Ian Granger was right all along and that you were duped?’

‘Yes.’

‘You didn’t meet anyone, see anyone, receive any new information before experiencing this Damascene conversion?’